Advances in integrated circuit technology have reduced the spacing between metal lines on a given layer and between interconnected lines in different layers of an integrated circuit. Such reduced spacing between metal lines results in an increase in capacitive coupling between nearby conductive traces, causing problems such as greater cross-talk and higher capacitive losses. In an effort to address these issues, low-k and ultra-low k (ULK) dielectric materials have been developed as a replacement for conventional dielectric materials used between conductors on a given layer and between layers. These materials can significantly reduce capacitive coupling between the conductors as compared to conventional dielectric materials.
One class of proposed materials relies on the dielectric constant of air (1.001) to achieve their low-k or ULK properties. With these materials, a porous dielectric layer is formed on the semiconductor surface. The effective dielectric constant of the material can be increasingly reduced with an increase in total pore volume of pores in the layer. However, at the same time the pores reduce the dielectric constant of the material, they undesirably also decrease the mechanical strength and stability of the layer, making it susceptible to damage during subsequent processing, for example, during patterning, deposition, chemical mechanical planarization or other processes. In addition, owing to their porous nature, the materials can be highly sensitive to contact with chemicals during subsequent processing such that device failure can result.
In an effort to address these problems, techniques of filling the pores with a sacrificial organic polymer have been proposed for purposes of providing mechanical strength during subsequent processing before the polymer is removed. Frot et al, Adv. Mater. 2011, 23, 2828-2832, describes such a process using PMMA-type, polystyrene-type, poly(propylene oxide) derivative or poly(ethylene oxide) derivative polymers. Known pore-filling materials can have poor thermal stability at elevated temperatures typically used for wafer processing. The inventors have recognized the desirability of a pore-filling composition having one or more of: good polymer flexibility and flow characteristics for a substantially void-free pore-fill, and good thermal stability at elevated process temperatures to avoid premature thermal decomposition during treatment and possible reliability problems resulting therefrom.
Accordingly, there is a continuing need for improved pore-filling compositions and methods which address one or more problems associated with the state of the art.